Flow simulation of a natural polymer in a syringe-needle delivery device

Neurodegenerative diseases, such as Parkinson's disease, affect a large num- ber of the erderly population and still remain untreated. In recent years, cell therapy has emerged as a promising therapeutic strategy. To increase cell viability, biomaterials are of- ten used as scaffolds and facilitate cell deposition, through injection, to the site of interest. However, fluid forces acting on the cells during injection may lead to their disruption or death. This study aims to develop a novel device for the delivery of a cell-embedded, in situ forming, collagen hydrogel. A preliminary simulation study on constricted channels rep- resenting the syringe was performed to gain insight into the effect of needle diameter and syringe geometry. Straight needles emanating co-axially from syringes of various geome- tries were computationally modelled in the two-dimensional space, using OpenFOAM^Ⓡ. The natural collagen solution was modelled as a continuum medium, without cells, and the flow was assumed incompressible, with non-Newtonian fluid constitutive behaviour. The effects of needle diameter and syringe geometry on velocity and shear stresses were examined. The results highlight the importance of geometric characteristics on the design of new cell delivery devices. If cells pass from the syringe barrel to the needle, the pressure drop and the increased velocity could damage them. This is more likely to occur using higher Gauge needles. Further analysis is required including simulations of cells during injection and analysis of their deformation.